The purpose of this research program is to investigte the early stages of language development by identifying the communicative and cognitive processes that underlie the emergence of symbolic behavior. Using an animal model, the proposed research will consist of an analysis of the linguistic development of Chantek, a five and a half year old male orangutan learning to communicate with gestural signs based on pidgin Sign English. After four and a half years of training by a small staff of caregivers, Chantek has acquired 95 signs and has steadily increased variety, spontaneity and complexity of his signed communications. The proposed research will continue the monitoring of Chantek's development and will include the expansion of his vocabulary. New areas of investigation related to the controversies that have arisen regarding animal models in this area of research will be studied, including double blind testing, studies of displacement, reference, semantics, and deception. Tool use and other cognitive areas will also be studied. This research will help to: 1) determine if and how the process of symbolization occurs, 2) assess the communicative and cognitive abilities of apes, 3) evaluate the orangutan as a linguistic and cognitive animal model and 4) suggest therapeutic strategies for language-impaired children by identifying elements related to the development of a symbolic capacity.